FILE - In this Sunday, April 8, 2018 file photo Spain's Rafael Nadal reacts after defeating Germany's Alexander Zverev 6-1, 6-4, 6-4 during a World Group Quarter final Davis Cup tennis match between Spain and Germany at the bullring in Valencia, Spain. For now, Nadal doesn’t see himself skipping Wimbledon the way Roger Federer has the French Open. The two veterans are back at the top of world tennis, with Nadal needing to win this week’s Monte Carlo Masters to avoid losing his top ranking once again to Federer in their seemingly eternal battle for tennis supremacy. (AP Photo/Alberto Saiz, File)

FILE - In this Sunday, April 8, 2018 file photo Spain's Rafael Nadal reacts after defeating Germany's Alexander Zverev 6-1, 6-4, 6-4 during a World Group Quarter final Davis Cup tennis match between Spain and Germany at the bullring in Valencia, Spain. For now, Nadal doesn’t see himself skipping Wimbledon the way Roger Federer has the French Open. The two veterans are back at the top of world tennis, with Nadal needing to win this week’s Monte Carlo Masters to avoid losing his top ranking once again to Federer in their seemingly eternal battle for tennis supremacy. (AP Photo/Alberto Saiz, File)

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia reaches for a backhand against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia celebrates after match point against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland waves to the crowd while leaving the court after his match against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland hits a backhand against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland hits a forehand against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia (L) shakes hands with Roger Federer of Switzerland (R) after their match on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia hits a backhand against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia reaches for a backhand against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia hits a backhand against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia reaches for a backhand against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland hits a backhand against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland hits a forehand against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia (L) shakes hands with Roger Federer of Switzerland (R) after their match on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland hits a backhand against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia celebrates after match point against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland waves to the crowd while leaving the court after his match against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Mandatory Credit: Geoff Burke-USA TODAY Sports

Roger Federer, of Switzerland, wipes his face during his match against Thanasi Kokkinakis, of Australia, at the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, of Switzerland, wipes his face during his match against Thanasi Kokkinakis, of Australia, at the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland waves to the crowd while leaving the court after his match against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland waves to the crowd while leaving the court after his match against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland smiles after a point against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia celebrates after match point against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Fans hold a banner in the stands between games during the match between Thanasi Kokkinakis of Australia and Roger Federer of Switzerland (both not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Tennis: Miami Open

Mar 24, 2018; Key Biscayne, FL, USA; Thanasi Kokkinakis of Australia celebrates after match point against Roger Federer of Switzerland (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Mar 24, 2018; Key Biscayne, FL, USA; Roger Federer of Switzerland waves to the crowd while leaving the court after his match against Thanasi Kokkinakis of Australia (not pictured) on day five of the Miami Open at Tennis Center at Crandon Park. Kokkinakis won 3-6, 6-3, 7-6(4). Mandatory Credit: Geoff Burke-USA TODAY Sports

Roger Federer, of Switzerland, waves to the crowd after Thanasi Kokkinakis, of Australia, defeated him in a tennis match at the Miami Open, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)

Roger Federer, of Switzerland, waves to the crowd after Thanasi Kokkinakis, of Australia, defeated him in a tennis match at the Miami Open, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)

Thanasi Kokkinakis, of Australia, reacts after defeating Roger Federer, of Switzerland, in a tennis match at the Miami Open, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)

Thanasi Kokkinakis, of Australia, reacts after defeating Roger Federer, of Switzerland, in a tennis match at the Miami Open, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)

Thanasi Kokkinakis, of Australia, celebrates after defeating Roger Federer, of Switzerland, in a tennis match at the Miami Open, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)

Thanasi Kokkinakis, of Australia, celebrates after defeating Roger Federer, of Switzerland, in a tennis match at the Miami Open, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Wilfredo Lee)

File photo: Federer of Switzerland at the U.S. Open Championships tennis tournament in New York

File photo: Roger Federer of Switzerland at the U.S. Open Championships tennis tournament in New York, September 13, 2015. REUTERS/Eduardo Munoz

Thanasi Kokkinakis, of Australia, reacts after getting a break point against Roger Federer, of Switzerland, during the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Thanasi Kokkinakis, of Australia, reacts after getting a break point against Roger Federer, of Switzerland, during the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, of Switzerland, walks to his chair during his match against Thanasi Kokkinakis, of Australia, during the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, of Switzerland, walks to his chair during his match against Thanasi Kokkinakis, of Australia, during the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, of Switzerland, pauses on the court during his match against Thanasi Kokkinakis, of Australia, at the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, of Switzerland, pauses on the court during his match against Thanasi Kokkinakis, of Australia, at the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, of Switzerland, goes to the net against Thanasi Kokkinakis, of Australia, during the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, of Switzerland, goes to the net against Thanasi Kokkinakis, of Australia, during the Miami Open tennis tournament, Saturday, March 24, 2018, in Key Biscayne, Fla. (AP Photo/Lynne Sladky)

Roger Federer, left, and Rod Laver pose for a portrait in silhouette after a promotional news conference for the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer, left, and Rod Laver pose for a portrait in silhouette after a promotional news conference for the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer watches a highlight video from the 2017 Laver Cup during a promotional news conference for the 2018 tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer watches a highlight video from the 2017 Laver Cup during a promotional news conference for the 2018 tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer, left, and Rod Laver pose for a portrait in silhouette after a promotional news conference for The Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer, left, and Rod Laver pose for a portrait in silhouette after a promotional news conference for The Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Rod Laver, second from left, responds to a question while promoting The Laver Cup tennis tournament with John McEnroe, left, Roger Federer and Nick Kyrgios, right, Monday, March 19, 2018, in Chicago. (AP Photo/Charles Rex Arbogast)

Rod Laver, second from left, responds to a question while promoting The Laver Cup tennis tournament with John McEnroe, left, Roger Federer and Nick Kyrgios, right, Monday, March 19, 2018, in Chicago. (AP Photo/Charles Rex Arbogast)

Roger Federer poses for a selfie after promoting the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer poses for a selfie after promoting the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

John McEnroe, left, responds to a question while promoting the Laver Cup tennis tournament with Rod Laver, second from left, Roger Federer and Nick Kyrgios Monday, March 19, 2018, in Chicago. (AP Photo/Charles Rex Arbogast)

John McEnroe, left, responds to a question while promoting the Laver Cup tennis tournament with Rod Laver, second from left, Roger Federer and Nick Kyrgios Monday, March 19, 2018, in Chicago. (AP Photo/Charles Rex Arbogast)

Roger Federer, left, and Nick Kyrgios watch a highlight video from the 2017 Laver Cup during a promotional news conference for the tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer, left, and Nick Kyrgios watch a highlight video from the 2017 Laver Cup during a promotional news conference for the tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer, second from right, responds to a question while promoting the Laver Cup tennis tournament with from left, John McEnroe, Rod Laver and Nick Kyrgios Monday, March 19, 2018, in Chicago. (AP Photo/Charles Rex Arbogast)

Roger Federer, second from right, responds to a question while promoting the Laver Cup tennis tournament with from left, John McEnroe, Rod Laver and Nick Kyrgios Monday, March 19, 2018, in Chicago. (AP Photo/Charles Rex Arbogast)

Rod Laver, left, and John McEnroe, center, take a photo and selfie next to Anish Kapoor's reflective sculpture Cloud Gate, in Chicago's Millennium Park as Roger Federer looks at the piece of art after promoting the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Rod Laver, left, and John McEnroe, center, take a photo and selfie next to Anish Kapoor's reflective sculpture Cloud Gate, in Chicago's Millennium Park as Roger Federer looks at the piece of art after promoting the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September. (AP Photo/Charles Rex Arbogast)

Roger Federer checks a photo he took next to Anish Kapoor's silver reflective sculpture Cloud Gate in Chicago's Millennium Park after promoting the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September.(AP Photo/Charles Rex Arbogast)

Roger Federer checks a photo he took next to Anish Kapoor's silver reflective sculpture Cloud Gate in Chicago's Millennium Park after promoting the Laver Cup tennis tournament Monday, March 19, 2018, in Chicago. The international tennis tournament will come to Chicago in September.(AP Photo/Charles Rex Arbogast)

Juan Martin del Potro, of Argentina, poses with his trophy after defeating Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, poses with his trophy after defeating Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, poses with his trophy after defeating Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, poses with his trophy after defeating Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Roger Federer, of Switzerland, reacts to losing a point to Juan Martin del Potro, of Argentina, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Roger Federer, of Switzerland, reacts to losing a point to Juan Martin del Potro, of Argentina, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, hits a backhand to Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, hits a backhand to Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, runs down a shot from Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, runs down a shot from Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, holds up his trophy after defeating Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)

Juan Martin del Potro, of Argentina, holds up his trophy after defeating Roger Federer, of Switzerland, during the men's final at the BNP Paribas Open tennis tournament, Sunday, March 18, 2018, in Indian Wells, Calif. Del Potro won 6-4, 6-7 (8), 7-6 (2). (AP Photo/Mark J. Terrill)